1. Field of the Invention
This invention generally relates to a vibration-resistant wind turbine, and is specifically concerned with a wind turbine having a rotor with at least two blades, each of which includes an inclinometer arrangement with at least two axes, and a process of operation.
2. Description of Related Art
Wind turbines typically comprise a rotor—with a hub and three rotor blades—that is mounted in horizontal orientation in an engine housing. The housing accommodates a rotor-driven generator and is mounted to rotate on a tower. In general, the rotor blades are mounted in an adjustable manner on the rotor hub to control the angle of attack of each individual rotor blade separately. In current research, it is even considered to also adjust parts of the rotor blade separately. By such an adjustment of the angle of attack (also referred to as pitch angle), the speed of the rotor can be regulated.
Wind turbines are basically subject to vibration, in particular because of the rotor being out of balance. The imbalances that occur are due primarily to either mass imbalances or aerodynamic imbalances. Mass imbalances may arise because of unequal rotor blade masses or unequal mass distributions in the individual rotor blade, hub imbalances, eccentricities of the complete rotor, icing on the rotor blades, or water penetration inside the rotor blades. Aerodynamic imbalances may arise because of blade angle errors, unequal rotor blade profile shapes, rotor blade damage, oblique inflow of the rotor, as well as site-based excitations from outside, (e.g., by tower resonance and the fact that the wind speed generally depends on the height above ground such that one and the same rotor blade is exposed to different aerodynamic forces, depending on whether it is just below or above). Such imbalances result in a reduced service life of the wind turbine. Minimization of the imbalances of the rotor is therefore desirable. Also, a diagnosis of the operating state of the wind turbine is advantageous in order to shut down the wind turbine for safety reasons when unacceptable stresses occur or to determine defective components and to exchange them in a timely fashion.
A survey on the vibration problem in wind turbines can be found in, for example, the magazine telediagnose.com, Edition No. 12.
Described in German Patent Application DE 102 19 664 A1 and corresponding U.S. Pat. No. 6,940,186 is a wind turbine in which sensor elements are provided for determining mechanical stresses of the rotor on the rotor blades and on the rotor shaft in order to adjust the rotor blades based on the mechanical stresses that are determined. The sensors that are provided on the rotor shaft are used to detect pitch and yaw moments. Also, the rotor blades can be provided with ballast tanks in order to pump water from a storage tank provided in the hub into the ballast tanks or to drain water from the ballast tanks into the storage tank in order to minimize possible rotor imbalance by trimming. While the filling of the ballast tanks is possible even during operation, the rotor in the corresponding position has to be shut down when draining a ballast tank.
From German Patent Application DE 10 2004 014 992 A1, a wind turbine is known in which an imbalance sensor is provided to determine the imbalance of the rotor, and the rotor blades are provided with balance weights that can be adjusted in axial direction and that can be adjusted corresponding to the determined imbalance in order to minimize the imbalance of the rotor.
In general, European Patent Application EP 1 674 724 A2 and corresponding U.S. Publication No. 2006/0140761 describes the monitoring of components of a wind turbine by means of various sensors, for example acceleration sensors, gyroscopes, proximity sensors, and inclinometers, and, in reference to the monitoring of rotor blades, the use of proximity sensors—by means of which the bending of the blades is to be detected—is described.
International Patent Application Publication WO 01/33075 A1 and corresponding U.S. Pat. No. 6,619,918 describes the load-sensing equipment of strain gauges attached to the rotor blades of a wind turbine for the purpose of controlling the pitch adjustment of the blades.
International Patent Application Publication WO 2006/012827 A1 and corresponding U.S. Publication No. 2008/0206052 describes the monitoring of the state of the rotor blades of a wind turbine during operation by means of solid-borne sound conduction, whereby movement sensors are arranged on the blades.
International Patent Application Publication WO 2006/039903 A1 and corresponding U.S. Patent Publication No. 2008/0067814 describes a pitch adjustment of the rotor blades of a wind turbine implemented by monitoring the pressure difference between the front side of the blade and the back side of the blade.
International Patent Application Publication WO 2007/131489 A1 and corresponding U.S. Publication No. 2009/031199 describes the use of acceleration sensors on the rotor blades of a wind turbine for the purpose of regulating the pitch angle, whereby vibration measurements are made.
International Patent Application Publication WO 2008/058876 A2 describes that for the purpose of preventing rotor blades from colliding with the tower of a wind turbine, distance sensors can be arranged on the tower or on the housing in order to measure the distance from the respective rotor blade to a prescribed location of the wind turbine and optionally to emit a collision warning.
International Patent Application Publication WO 2005/068834 A1 and corresponding U.S. Publication No. 2007/0297892 relates to a wind turbine in which the state of the rotor blade is monitored by means of strain gauges, and the position of the rotor blade is monitored by means of GPS.
The monitoring of the state of the rotor blades by means of strain gauges is problematic in as much as strain gauges are difficult to install and are relatively short-lived. Furthermore, strain gauges measure, in principle, only locally in the structure of the rotor blade. This shortcoming also applies to acceleration sensors or movement sensors.